AT89LP428 datasheet(70/149 Pages) ATMEL

70 / 149 page

3654A–MICRO–8/09

AT89LP428/828

Figure 13-8. Asymmetrical (Edge-Aligned) PWM

13.4.2

Symmetrical PWM

For Symmetrical PWM, Timer 2 should be configured for Auto-reload mode and Count Mode 2

or 3 (CP/RL2 = 0, DCEN = 0, T2CM1-0 =1xB). Symmetrical PWM uses dual-slope operation as

shown in Figure 13-9. The timer counts up from MIN to TOP and then counts down from TOP to

MIN. The timer is equal to TOP for exactly one clock cycle. In non-inverting mode, the output

CCx is cleared on the up-count compare match between Timer 2 (TL2, TH2) and the channel

data register (CCxL, CCxH), and set at the down-count compare match. In inverting mode, the

output CCx is set on the up-count compare match between Timer 2 and the data register, and

cleared at the down-count compare match. The resulting symmetrical PWM output waveform is

center-aligned around the timer equal to TOP point. Symmetrical PWM may be used to generate

non-overlapping waveforms.

The TOP value in RCAP2L and RCAP2H is double buffered such that the output frequency is

only updated at the underflow. The channel data register (CCxL, CCxH) is also double-buffered

to prevent glitches. The output frequency and duty cycle for symmetrical PWM are given by the

following equations:

The extreme compare values represent special cases when generating a PWM waveform. If the

compare value is set equal to (or greater than) TOP, the output will remain high or low for non-

inverting and inverting modes, respectively. If the compare value is set to MIN (0000H), the out-

put will remain low or high for non-inverting and inverting modes, respectively.

{RCAP2H,RCA2L}

CP/RL2 = 0, T2CM1-0 = 01B, DCEN = 0

Inverted

{CCxH,CCxL}

Non-inverted

CCx

OUT

Oscillator Frequency

RCAP2H RCAP2L

}

-----------------------------------------------------------------

TPS

---------------------

Non-Inverting:

Duty Cycle

100%

CCxH CCxL

}

RCAP2H RCAP2L

}

------------------------------------------------------

Inverting:

Duty Cycle

100%

RCAP2H RCAP2L

}

CCxH CCxL

}

–

RCAP2H RCAP2L

}

---------------------------------------------------------------------------------------------------

AT89LP428 Arkusz danych(PDF) 70 Page - ATMEL Corporation

AT89LP428 Arkusz danych(HTML) 70 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Arkusz danych Pobierz

Link URL